I have recently been experiencing problems with "Line 2" on my main electrical panel. A few times, "Line 2" was not showing any incoming power when "Line 1" looked fine.

Now, I'm having a hard time getting AC to the bus. My Progressive Industries protector at the post shows 120 volts each leg and no errors.

I turn on the main breaker in the outside bay on the transfer switch and everything is OK. Power transfers to the inside panel.

However, as soon as much of a load is applied (a single air conditioner, water heater, etc.) the power drops out. Although the main breaker doesn't appear "tripped" on the transfer switch box, when I turn it off and then back on power is restored to my inside panel.

Everything seems fine under generator power.

Any suggestions? I need to resolve this ASAP as I expect to be deployed to Texas as part of an insurance adjusting team.

Should I first try replacing the main breaker on the transfer switch box? or do the symptoms appear more related to "something" going on with the transfer switch proper?

Thanks for the help!